Ball mill



F. E. MARCY May 3, 1938.

BALL MILL Filed July 27, 1936 4 Sheets-Sheet 1 May 3, 1938. F. E. MARCY BALL MILL Filed July 27, 1936 4 S hQets-Sheet 2 May 3, 1938. E MARCY 2,115,820

BALL MILL Filed July 27, 1936 4 Sheets-Shget 3 Patented May 3, 1938 UNITED .STATES PATIENT" OFFICE ausszo Frank 1:. fist f me, Application Ill 27, 1936, Serial No. 92,887-

' 3 Claims. (cast-9) This invention relates to ball mills and is particularly directed to improvements in means for discharging materials from ball mills.

A principal object or the invention is the provision of means for the discharge of materials from ball mills whereby the content of material in the mill may be maintained substantially constant at a predetermined amount regardless of fluctuations or surges in the feed to the mill or in other operating conditions.

A further object of the invention is to provide ball mills having discharge means of simple and rugged construction which are efiective and dependable in their operation.

Another object -of the invention is the provision of means for the discharge of materials from ball mills whereby the height of the discharge may be varied to a substantial degree without ailecting the level of the material in the ball mill. i 7 Other objects and advantages of the invention will be apparent from the detailed description of illustrative embodiments of the invention hereinafter appearing. 25 The, invention is particularly valuable in connection with ball mills operated with a relatively small mill content or with a low pulp line, which has been found by a number of yearsoi. experiment and practical operation to be the condition under which ball mills operate at the greatest capacity and efdciency.

The invention will'be more particularly described for thepurpose of illustration with reference to the accompanying drawings in which:

Fig. 1 is a fragmentary elevation in partial section of the discharge end of a ball mill embodying the principles of the invention;

Fig. 2 is an end elevation of the embodiment shown in Fig. 1 with the end plate removed;

Fig. 3 is a front elevation and Fig. 4 is a side elevation of a discharge grate section of the form shown in Figs. 1 and 2;

Fig. 5 is a fragmentary view in partial section showing a detail of the discharge grate section 45 of Figs. 3 and 4;

Fig. 6 is an elevation of a bottom closure mem-' ber;

- Fig. '7 is a perspective view of an angle brace of the'embodiment of Figs. 1 and 2;

Fig. 8 is a fragmentary elevation of the discharge end of a ball mill provided with a modifled form of discharge grate;

Fi 9 is a fragmentary sectional view of the form of the invention shown in Fig. 8, taken on the line 99 of Fig. 8;

Fig. 10 is an elevation and Fig. 11 is a side view of a three-scoop discharge device which may be used in connection with the ball mills of Figs. 1 and 10; j m

Fig. 12 is an end view and Fig. 13 is an elevation of another form of discharge grate embodying the principles of the invention;

m Fig. 14 is a fragmentary section on line [4- of Fig. 13; and I Fig. 15 is a fragmentary partial section on line i5l5 of Fig. 14. 1

In Figs. 1 and 2, I6 is the shell of a ball mill provided at the discharge end with a drilled flange ii, and hawng an annular boss l2 on which is mounted a tire I 3 whereby the mill is supported for rotation upon rollers it. The mill is driven by conventional means, not shown, which may be located at the feed end of the mill. Inside the shell are provided liner membersv i5, and adjacent the end of the shell there is provided the discharge grate assembly it.

The discharge grate assembly includes a plurality of grate sectors i7, shown in further detail in Figs. 3-5, connected by means described hereinafter into a strong, rugged annular grate, readily removable for repairs and replacements.

The grate sectors ll, comprise a plurality of rolled steel bars l8, positioned in parallel alignment and in suitable spaced relation by means of side plates I 9 to which the bars are welded. The positioning of the hers is aided and the structure is strengthened by spacing pads 28 suitably placed between and welded to adjacent plates. The sector is further strengthened by means of rods 20 which may be welded to both the bars and the side plates. As is indicated, the

side plates l9 "project beyond thegrate bars on the discharge side thereof and serve for attaching thesectors to the shell of the mill and for connecting them together into the grate assemblies. The sectors are advantageously connected to the shell by means of angle braces 2| (see Fig. '1) the bolts 22 attaching the braces to the sectors also serving to connect adjacent sectors together at their peripheral ends. The central ends of the sectors are similarly connected by bolts 23 passing through side plates IQ of adjacent sectors and advantageously the same bolts pass through lugs 25 of an annular center plate 28.

The space between the peripheral ends of the sectors and the shell Ill oi the mill is closed by clamp bars 26 (see Fig. 6) thrust against the peripheral end bars of the grate sectors by means of screw bolts 2?.

A particularly valuable feature oi the grate of the invention is'the progressive variation in the openings between the bars which has been found to be very advantageous in-maintaining a substantially constant pulp level in the ball-mill; By increasing the width of the openings in the grates towards the center of the grate the rate of discharge increases very rapidly as the pulp level rises and clogging of the mill with surges in the feed or other variations in operating cona may advantageously be inch, the next inch,

and increasing progressively to H inch at the central end. In general, the openings between the grate bars may be varied from openings of, for example, to inch at the peripheral end to openings of, for example, to inch at the central end of the sectors.

Where the specification and claims refer to the progressive variation in the width of the slots in the grate, this shall include structures in which each slot varies in width from an adjacent slot as well as those in which the progression is in stages with several slots in each stage of the same width.

The material flowing through the grate may advantageously be discharged, for example, to a launder not shown, through an annular opening at the periphery of the discharge end of the shell formed between the annular spout member 29 and end plate 30 spaced from the spout memberby means of spacers 3| or bolts 32 which fasten both the spout member and the end plate to flange Ii of shell "I.

The door 33, centrally located in end plate 30, provides an advantageous means for inspecting the discharge grate during operation of the ball mill. The door can be removed or replaced during operation by pressing button 34 in handle 35, which retracts catches 36 through levers 31. The catches when extended engage the inside of the circular opening in door 3 or any suitable circular holder mounted thereon.

If it is desired to discharge the eiliuent from. the ball mill at a point above the bottom of the mill the spout member 29 and end plate 30 may be replaced by a scoop discharge device such as is shown in Figures 10 and 11. This device is shown by way of example with three scoops ll, which lift efiluent material from the peripheral wall 42 and discharge it through the central spout 43. The outer wall of the discharge device is advantageously provided with hand-holes 44. By the use of this device the ei'fluent material may be discharged at within or 6 inches below the center of the mill.

Figs. 8 and 9 show a one-piece grate 56 which may replace the grate assembly l6 shown in Figs. 1 and 2, and which includes a number of valuable improvements. The grate consists of a single annular member, having an external diameter slightly less than the internal diameter of the shell ill of the ball mill. It is provided with a plurality of slots 5| cut or cast therein. The slots are arranged in a plurality of segmental groups. They extend along chords of the annular grate and may be designated as chordal slots. The slots 5! preferably vary in width from the periphery towards the center, as described in connection with Figs. 3-5.

The grate may be attached to the shell of the mill by means of bolts 52 passing through holes in lugs 53 spaced about the periphery of the grate. The grate is tightly positioned by means of wedges 54 which are preferably bifurcated to fit around bolts 52. These wedges greatly facilitate the installation and removal of the grates.

An advantageous feature of the grate shown in Figs. 8 and 9 is the provision of a wear-compensating annular bulge or convexity 55, the thickness of which is proportioned to the normal amount of wear on the grate ends at various points along the radius.

The center of the grate is preferably left open to provide a manhole which may be closed by a manhole cover 56 bolted to the grate.

A further form of grate sector is shown in Figs. 12 to 15. In this form of sector the bars 6| are welded in spaced parallel relation to side plates 62 which are positioned at an angle of approximately 66 to the longitudinal faces of the bars. Spacing pads 63 are provided as in the grate sector shown in Figs. 3-5, and rods 64 welded to the bars and side plates further strengthen the sectors. The bars are preferably spaced at distances increasing from the periphery towards the center ,as described in connection with Figs. 3-5.

The sectors may be connected into a grate assembly by means of a spider and suitable con necting elements as shown in my U. S. Patent No. 1,629,803.

I claim:

1. Discharge means for ball mills adapted to automatically regulate the rate of discharge so as to maintain a substantially constant low level of material in the mill regardless of variation in the rate of feed comprising a grate member mounted adjacent the discharge end of the drum of the ball mill, said grate having a plurality of discharge openings in the form of elongated slots positioned with their longitudinal axes along chords of said drum, the width of the slots progressively increasing from the periphery of the drum towards the center and the slots adjacent the center being substantially wider than those adjacent the periphery whereby to substantially accelerate the discharge of material through the grate as the level of material rises in the drum above the desired low level.

2. A grate for ball mills adapted to automatically regulate the rate of discharge in relation to the height of material in the mill, said grate comprising a plurality of sector shaped units, each of said units comprising a pair of side members, a plurality of grate bar elements supported in spaced relation between said side members to deline a plurality of elongated slots, the spacing between said bars progressively increasing in width towards the inner end of the sector and the space between the bars adjacent said inner end being substantially greater than between the bars adjacent the outer end whereby the rate of discharge of material from the mill will be substantially increased with the rise of the level of material within the mill.

3. In a grate for ball mills adapted to automatically compensate for variations in the rate of feed by automatically regulating the rate of discharge in relation to the height of material in the mill, a grate sector comprising a pair of side members, a plurality of grate bar elements secured at their ends to said side members in spaced parallel relation, spacing pads secured between adiacent bars, said pads progressively increasing in thickness from the outer to the inner end of the sector and the space between said bars being correspondingly increased so that the space between the bars adjacent the inner end of the sector is substantially greater than between those adjacent the outer end thereof whereby the rate of discharge of material from the mill is substantially increased as the material in the mill rises above a desired level.

I 'RANK E. MARCY. 

